django.db.utils.OperationalError: (2003, "Can't connect to MySQL server on '127.0.0.1:3307' (111)") – Docker

I’ve setup my project Django REST API on GCP VM running Ubuntu 22.0.4 LTS in a virtual environment. I’m currently configuring the following open source Rest API project :
https://github.com/OkunaOrg/okuna-api

The Okuna CLI uses docker-compose to spawn and coordinate the following docker services.
webserver – A server running the Okuna API
db – A server with a MariaDB database
redis – A server with a Redis database
scheduler – A server responsible for running the scheduled Okuna jobs such as curating Explore/Top posts.
worker – A server responsible for processing the Okuna jobs such as publishing a post or curating posts

The Django backend opens up successfully at the GCP external IP address as configured by me in the okuna-cli.py. However I face problems when I run

python3.8 manage.py migrate

The Error trace

django.db.utils.OperationalError: (2003, "Can’t connect to MySQL server on ‘127.0.0.1:3307’ (111)")

The .env file(https://github.com/OkunaOrg/okuna-api/blob/master/templates/.env) has the following pertaining to the above error :

# [NAME] ALLOWED_HOSTS
# [DESCRIPTION] Django variable specifying allowed hosts.
# [REQUIRED][PRODUCTION]
# [MORE] https://docs.djangoproject.com/en/2.1/ref/settings/#allowed-hosts
# ALLOWED_HOSTS=openbook.social

# [GROUP] SQL Database Configuration
# [DESCRIPTION] The SQL database configuration
# [REQUIRED][ALWAYS]
RDS_DB_NAME=okuna
RDS_USERNAME=root
RDS_HOSTNAME=127.0.0.1
RDS_PORT=3307
RDS_HOSTNAME_READER=127.0.0.1
RDS_HOSTNAME_WRITER=127.0.0.1
# [NAME] RDS_PASSWORD
# [DESCRIPTION] The password for the SQL Database.
RDS_PASSWORD={{SQL_PASSWORD}}

# [GROUP] Redis Database configuration Configuration
# [DESCRIPTION] The redis database configuration
# [REQUIRED][ALWAYS]
REDIS_HOST=127.0.0.1
REDIS_PORT=6380
# [NAME] REDIS_PASSSWORD
# [DESCRIPTION] The password for the REDIS Database. If using okuna-cli, obtained from .okuna-cli.json
REDIS_PASSWORD={{REDIS_PASSWORD}}

The .docker-compose.env file(https://github.com/OkunaOrg/okuna-api/blob/master/templates/.docker-compose.env) has the following pertaining to the above error :

# [NAME] ALLOWED_HOSTS
# [DESCRIPTION] Django variable specifying allowed hosts.
# [REQUIRED][PRODUCTION]
# [MORE] https://docs.djangoproject.com/en/2.1/ref/settings/#allowed-hosts
# ALLOWED_HOSTS=openbook.social

# [GROUP] SQL Database Configuration
# [DESCRIPTION] The SQL database configuration
# [REQUIRED][ALWAYS]
RDS_DB_NAME=okuna
RDS_USERNAME=root
RDS_HOSTNAME=db.okuna
RDS_PORT=3306
RDS_HOSTNAME_READER=db.okuna
RDS_HOSTNAME_WRITER=db.okuna
# [NAME] RDS_PASSWORD
# [DESCRIPTION] The password for the SQL Database. If using okuna-cli, obtained from .okuna-cli.json
RDS_PASSWORD={{SQL_PASSWORD}}

# [GROUP] Redis Database configuration Configuration
# [DESCRIPTION] The redis database configuration
# [REQUIRED][ALWAYS]
REDIS_HOST=redis.okuna
REDIS_PORT=6379
# [NAME] REDIS_PASSSWORD
# [DESCRIPTION] The password for the REDIS Database.
REDIS_PASSWORD={{REDIS_PASSWORD}}

The settings.py file(https://github.com/OkunaOrg/okuna-api/blob/master/openbook/settings.py) has the following pertaining to the above error :

ALLOWED_HOSTS = os.environ.get('ALLOWED_HOSTS')
if IS_PRODUCTION:
    if not ALLOWED_HOSTS:
        raise NameError('ALLOWED_HOSTS environment variable is required when running on a production environment')
    ALLOWED_HOSTS = [allowed_host.strip() for allowed_host in ALLOWED_HOSTS.split(',')]
else:
    if ALLOWED_HOSTS:
        logger.info('ALLOWED_HOSTS environment variable ignored.')
    ALLOWED_HOSTS = ['*']   
    
REDIS_HOST = os.environ.get('REDIS_HOST', 'localhost')
REDIS_PORT = int(os.environ.get('REDIS_PORT', '6379'))
REDIS_PASSWORD = os.environ.get('REDIS_PASSWORD')    

Here is the docker-compose-full.yaml(https://github.com/OkunaOrg/okuna-api/blob/master/docker-compose-full.yml)

version: '3'

services:
  webserver:
    container_name: okuna-api
    build:
      dockerfile: Dockerfile
      context: ./.docker/api
    privileged: true
    extra_hosts:
      - db.okuna:172.16.16.4
      - redis.okuna:172.16.16.5
    volumes:
      - ./:/opt/okuna-api
      - ./.docker-cache/pip:/root/.cache/pip
    ports:
      - 80:80
    working_dir: /opt/okuna-api
    networks:
      okuna:
        ipv4_address: 172.16.16.1
    depends_on:
      - db
      - redis
    env_file:
      - .docker-compose.env
  worker:
    container_name: okuna-worker
    build:
      dockerfile: Dockerfile
      context: ./.docker/worker
    privileged: true
    extra_hosts:
      - db.okuna:172.16.16.4
      - redis.okuna:172.16.16.5
    volumes:
      - ./:/opt/okuna-api
      - ./.docker-cache/pip:/root/.cache/pip
    working_dir: /opt/okuna-api
    networks:
      okuna:
        ipv4_address: 172.16.16.2
    depends_on:
      - webserver
    env_file:
      - .docker-compose.env
  scheduler:
    container_name: okuna-scheduler
    build:
      dockerfile: Dockerfile
      context: ./.docker/scheduler
    privileged: true
    extra_hosts:
      - db.okuna:172.16.16.4
      - redis.okuna:172.16.16.5
    volumes:
      - ./:/opt/okuna-api
      - ./.docker-cache/pip:/root/.cache/pip
    working_dir: /opt/okuna-api
    networks:
      okuna:
        ipv4_address: 172.16.16.3
    depends_on:
      - webserver
    env_file:
      - .docker-compose.env
  db:
    image: mariadb:10.4.5
    hostname: db.okuna
    volumes:
      - mariadb:/var/lib/mysql
    ports:
      - 3306
    privileged: false
    networks:
      okuna:
        ipv4_address: 172.16.16.4
    command: --character-set-server=utf8 --collation-server=utf8_unicode_ci
    env_file:
      - .docker-compose.env
  redis:
    image: bitnami/redis:latest
    privileged: false
    ports:
      - 6379
    networks:
      okuna:
        ipv4_address: 172.16.16.5
    env_file:
      - .docker-compose.env
    volumes:
      - redisdb:/bitnami/redis/data

volumes:
  mariadb:
  redisdb:

networks:
  okuna:
    ipam:
      driver: default
      config:
        - subnet: "172.16.16.0/16"

Need help here. Thanks.